kernel: Disable IXP4xx physmap by default

This makes no sense on anything but the IXP4xx platform
that we do not even support anymore. If we bring it back,
it can be selectively enabled for that platform only.

Signed-off-by: Linus Walleij <[email protected]>

target/linux/generic/config-5.10

@@ -3555,6 +3555,7 @@ CONFIG_MTD_OF_PARTS=y
 # CONFIG_MTD_PHYSMAP is not set
 # CONFIG_MTD_PHYSMAP_COMPAT is not set
 # CONFIG_MTD_PHYSMAP_GEMINI is not set
+# CONFIG_MTD_PHYSMAP_IXP4XX is not set
 # CONFIG_MTD_PHYSMAP_GPIO_ADDR is not set
 CONFIG_MTD_PHYSMAP_OF=y
 # CONFIG_MTD_PHYSMAP_OF_GEMINI is not set